Question

A $10kg$ ball is dropped from a height of $10m$. Find (a) the initial potential energy of the ball, (b) the kinetic energy just before it reaches the ground, and (c) the speed just before it reaches the ground.

Answer 1

(a)$PE=mgh$

$=10\times 10\times 10=1000J$

(b)Initial PE=final KE

Therefore KE just beofre it reaches the ground $=1000J$

(c)Final $KE=\frac{1}{2}m{v}^2=1000$

$v=\sqrt{\frac{2\times 1000}{m}}$

$=\sqrt{\frac{2000}{10}}=14.14m/s$